The D.C. Co-operative Extension Service, in co-operation with the city public libraries is offering two free courses on growing plants indoors. The times and locations for the first course, titled "The Science of Growing Plants Indoors," are:

Chevy Chase library, Connecticutt near McKinley NW, Mondays from 10 A.M. till noon Monday and Apr. 4, 11, 18 and 25.

Park View recreation center, Warder Street and Otis Place, NW. Tuesdays from 7 to 9 p.m. Tuesday and April 5, 12 and 19.

Please register by calling 282-7403. Give your name, phone number and which section you plan to attend. Preference will be given to those who register in advance if classes are filled to capacity.

Subjects to be covered include soils, light, fertilizer, watering, propagation, dish gardens, terrariums, hanging baskets and more.

The second course is a two-hour program on spring care of houseplants. The location and times are:

Chevy Chase library, Connecticut Avenue near McKinley Street NW, Thursday, Apr. 14, 7 to 9 p.m.

Woodbridge library, Rhode Island Avenue and 18th Street NE, Saturday, April 16, 10 a.m. to noon.

Tenley Friendship library, Wisconsin Avenue and Albemarle Street NW, Wednesday, Apr. 20, 7 to 9 p.m.